In its simplest form of a screw compressor which includes a slide valve, attention is directed to U.S. Pat. No. 3,088,659 to Nilsson et al, dated May 7, 1963, in which a pair of coacting male and female rotors are mounted on parallel axes and in the lower portion of the housing and intersecting the bores within which the rotors operate, a slide valve is mounted and is operated by a shaft extending from one end of the valve through the housing for operation by conventional means to regulate the pressure of the fluid compressed or pumped by the rotors. It will be seen from the disclosure of this patent that it is customary for the slide valves to be mounted within a cylindrical bore that intersects the cylindrical bores within which the male and female rotors operate. Due to the fact that very substantial pressures are exerted against the slide valve, there is a tendency for wear to develop between the surfaces of the slide valve which engage the cylindrical bore in which it is reciprocable for adjusting the operation of the compressor, particularly in regard to the pressures generated thereby as referred to above.
As far as has thus far been determined, the only attempt to minimize the friction and consequent wear normally occurring between a slide valve in a compressor of the aforementioned type and the cylindrical bore in which it operates, is disclosed in U.S. Pat. Nos. 3,734,653, to Edstrom et at, dated May 22, 1973, and 3,738,780, to Edstrom, dated June 12, 1973, the improvements offered by these patented constructions, however, pertaining to lubrication alone, rather than any attempt to provide anti-friction support or the like, as in the instant invention.
Further, various developments have been made heretofore with respect to guiding the slide valve of screw-type compressors and one such example is shown in prior U.S. Pat. No. 3,432,089 to Schibbye, dated Mar. 11, 1969, said patent being representative of a number of other patents disclosing various support and guide means for the slide valve but none of which have been found to include anti-friction means.